Separation of Content, Presentation, and Interaction
There is a sliding scale, not a black/white split, between highly abstract and highly concrete representations, with a progressive loss of restyling flexibility and a progressive increase in design input.
Language designers SHOULD design formats that allow authors to separate content from presentation and interaction concerns.
This is just the tip of the iceberg. Traditional methods of editing ands serving the same resource and using flexible client-side styling now complemented by server-side preprocessing, client capability preferences, delivery contexts.